题目

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.

这道题比较经典了，就是有点像编译器判断代码符号是否符合规则，是堆栈的一个简单应用。当遇到"{","[","("的时候入栈，如果遇到这些符号的另一半，则取栈顶比较，如果是一对就继续，不然返回false。

代码

public class Solution {public boolean isValid(String s) {if(s.length()==0) return true;int len=s.length();char[] symbolFirst={'(','{','['};char[] symbolSecond={')','}',']'};char strChar[]=s.toCharArray();     Stack sym=new Stack();for(int i=0;i<len;i++){for(int j=0;j<symbolFirst.length;j++){if(strChar[i]==symbolFirst[j]){if(len==1){return false;}sym.push(strChar[i]);}               }for(int k=0;k<symbolSecond.length;k++){if(strChar[i]==symbolSecond[k]){if(sym.isEmpty()){return false;}else{if(!sym.peek().equals(symbolFirst[k])){return false;   }else{sym.pop();}}}}}if(sym.isEmpty()){return true;}else{return false;}   }
}

代码下载：https://github.com/jimenbian/GarvinLeetCode

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【LeetCode从零单排】No20.ValidParentheses

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